Before spilling a live range, we split it into a separate range for each basic
block where it is used. That way we only get one reload per basic block if the
new smaller ranges can allocate to a register.

This type of splitting is already present in the standard spiller.

llvm-svn: 110934

llvm-svn: 110720

When splitting a live range, the new registers have fewer uses and the
permissible register class may be less constrained. Recompute the register class
constraint from the uses of new registers created for a split. This may let them
be allocated from a larger set, possibly avoiding a spill.

llvm-svn: 110703

during live range splitting.

llvm-svn: 110686

necessary.

Sometimes, live range splitting doesn't shrink the current interval, but simply
changes some instructions to use a new interval. That makes the original more
suitable for spilling. In this case, we don't need to duplicate the original.

llvm-svn: 110481

After heavy editing of a live interval, it is much easier to simply renumber the
live values instead of trying to keep track of the unused ones.

llvm-svn: 110463

llvm-svn: 110453

We are now at a point where we can split around simple single-entry, single-exit
loops, although still with some bugs.

llvm-svn: 110257

rewrite instructions for live range splitting.

Still work in progress.

llvm-svn: 109469

The spillers can pluck the analyses they need from the pass reference.

Switch some never-null pointers to references.

llvm-svn: 108969

Determine which loop exit blocks need a 'pre-exit' block inserted.
Recognize when this would be impossible.

llvm-svn: 108941

llvm-svn: 108845

This is a work in progress. So far we have some basic loop analysis to help
determine where it is useful to split a live range around a loop.

The actual loop splitting code from Splitter.cpp is also going to move in here.

llvm-svn: 108842